1. Field of Invention
This invention relates to improved methods for applying a reagent to an analytical test device. The test devices prepared by the methods of this invention are typically used to determine the presence and/or the quantity of an analyte in a liquid test sample, such as whole blood. This invention also provides apparatus for applying the reagent to the analytical test device.
2. State of the Art
Analytical test devices containing a reagent are commonly used to determine the presence or the quantity of a particular analyte in liquid samples, such as whole blood. For example, diabetics typically use such test devices to monitor the level of glucose in their blood. The reagent on the test device typically indicates the presence or the quantity of the analyte in the liquid sample using either spectrophotographic, color match or electrochemical technology. Such test devices generally comprise a substrate, such as a non-porous handle, and an absorbent test pad attached to the handle. The reagent is typically applied to the test pad either before or after assembly and then dried to create a "dry" chemical test device.
Numerous methods of applying reagents and coatings to analytical test devices have been described in the literature. These methods include dip coating, roll coating, ink jet application, screen printing, brushing, painting and the like.
For example, Bertek, Inc. literature entitled "The Technology of Coating and Laminating" (1986) describes various coating technologies and techniques, including roll coating, knife over roll and slot coating methods. These methods typically apply the reagents either across the whole web of the test device or in a continuous manner.
Similarly, U.S. Pat. No. 5,547,702 to Gleisner, describes a method of applying a reagent mixture down a reagent test pad in a continuous manner.
Many other patents describe imbibing processes such as dip coating processes. For example, U.S. Pat. No. 4,935,346 to Phillips et al., describes a process in which a membrane is dip coated and then dried.
When the test devices prepared by such methods are used to determine the quantity of an analyte in a liquid sample, it is particularly important that the amount of reagent deposited on the test device be accurately controlled so that reproducible test results are achieved. Additionally, the reagents employed in the test devices are often expensive and need to be conserved. Therefore, it is particularly important that the reagent be applied to the test device only where it is needed. Accordingly, it would highly desirable to develop novel methods and apparatus for applying the reagent to the test device such the reagent is deposited on the test device in an accurate and controlled manner.